in Xsetup , I had chosen yes for "Wheelmice use Imps/2 protocol", I have gone there and redone the setup at least 50 times, and then restarted "startx", hoping it will work at some point but it never did .

By restarting, did you exit X first?

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I don't understand why the scroll wheel doesn't work, when it works fine with other distros.

DSL uses the tinyx server by default, whereas most distros use a fully-featured one (it's also slightly older)... which could be an explanation. You could try one on DSL if you can't this to work. Or a newer tinyx server (see mydsl).